This invention relates to a torsionally installed sacrificial anode for galvanic corrosion protection of a metallic article (e.g., an underground pipeline, steel piling, underground residential electrical distribution equipment, etc.) from corrosion and, in other embodiments thereof, relates to a torsionally installed combination galvanic anode and earth anchor/penetrator for not only providing galvanic corrosion protection to an underwater metal object (e.g., an undersea pipeline), but also serves to mount the metal object above the seabed.
Generally, corrosion of metallic objects, such as underground and undersea pipelines, underground residential electrical distribution lines and equipment, underground steel tanks, bridge pilings, deep well casings, piling anchors for seawalls, and offshore structures, results when the base metal (usually steel) of the article comes into contact with an electrolyte solution (i.e., ground water or sea water) which contains positively charged hydrogen ions (H.sup.30 ) and negatively charged hydroxyl ions (OH.sup.-). When the following four conditions are met, a metallic object will corrode: 1.the presence of an anode and a cathode; 2.an electrical potential between the anode and the cathode; 3.a metallic (or electrical) path between the anode and the cathode; and 4.the anode and the cathode must be immersed in the electrolyte solution. When these conditions are met, an electrical current will flow and the metallic anode will be consumed. Of course, if the anode is a steel structural member, such as a pipeline or a part of the superstructure of an offshore oil well platform or bridge, serious structural damage may occur.
When the above-mentioned four conditions are met, an electric current will flow from the anode to the cathode and the base metal (e.g., the steel) will be consumed where the current leaves the base metal to enter the surrounding electrolyte. Typically, the current generated is small (usually measured in milliamps). However, even a very small current restricted to localized discharge points can cause severe deterioration to steel pipes and the like. Usually, however, the discharge surface of the base metal is spread out over a large area, thus slowing down the rate of corrosion, but corrosion nevertheless results along the entire length of the metallic structure exposed to the electrolyte. The electrical resistance of the anode-cathode electrolyte circuit and the formation (or the lack thereof) of polarization films on the magnetic article controls, to a large degree, the rate of corrosion. Thus, coating systems have long been employed in many applications to reduce the rate of corrosion, but such coatings are not suitable for overcoming all galvanic corrosion problems.
Another common type of corrosion protection system is referred to as cathodic protection utilizing galvanic, sacrificial anodes. By transforming the protected metal structure from an anode to a cathode, corrosion of the metal structure can be inhibited. In one instance, if steel is the base metal, an anode having a higher reduction or electromotive potential voltage, such as zinc, aluminum, or magnesium, is electrically connected to the steel base metal, the galvanic current flowing through the base metal will use the higher reduction potential or electromotive voltage potential metal as the anode which, over time, will be sacrificially destroyed so as to prevent corrosion to the base metal. In certain instances, a voltage is impressed on the base metal so as to ensure that the base metal remains the cathode with this impressed voltage overcoming a variety of factors, such as dissimilar soil conditions, dissimilar base metals, coatings, electrolyte differences, etc., which affect the anode/cathode current. Reference may be made to such prior U.S. Pat. Nos. as 2,053,214 and 3,548,643, which disclose such impressed voltage cathodic corrosion protection systems.
These sacrificial anodes are commercially available in a variety of configurations, depending on the particular application. For example, in an underground onshore pipeline application, the anodes may be located remotely from the pipeline a distance of several yards and connected thereto by electrical lead wires with the anodes being buried in the earth along with the pipeline. As these underground anodes are sacrificially consumed, it is necessary, usually over extended periods of time, to replace the anodes as they are consumed. This initial installation and periodic replacement of underground sacrificial anodes oftentimes requires substantial excavation and backfilling which, of course, requires considerable manpower and equipment.
On underwater or submerged structures, such as the frameworks of offshore oil well platforms, bridge piers, and undersea pipelines, the anodes are typically mounted on the metallic base structure at strategic locations by means of steel straps or the like imbedded in the aluminum or magnesium sacrificial anode, and the steel straps are welded to the steel structure so as to ensure good electrical continuity between the structure and the anode. In other applications, so-called standoff anodes are used in which the anodes are spaced about 4-6 inches (10-15 cm.) from the surface of the sealed structure by means of a standoff steel frame or the like which is welded to the structure.
In the installation of grounding wires and the like in, for example, electrical distribution systems, it is oftentimes desirable to provide a ground anode which provides a low electrical resistance to ground, but yet which has sufficient strength to be sucessfully driven into the earth. Reference may be made to the following list of prior U.S. patents for examples of various grounding rods or shoes in the same general field as at least one embodiment of the present invention: U.S. Pat. Nos. 642,169, 1,737,562, 2,157,180, 2,537,463, 3,522,359, 3,716,649, 3,817,852, 3,876,819, and 4,316,050. While the prior art grounding rods worked well for their intended purposes, they were somewhat difficult to install, as in many applications they required separate excavation and backfilling operations.
Because such sacrificial anodes require periodic replacement, there has been a long-standing need for an easily replaceable sacrificial anode, particularly where the anode is to be buried underground in remote areas (e.g., along a power line or pipeline in rural areas) or under the seabed.